Dead front fuse with improved terminal clamping means



ICL

Nov. 17, 1964 w. s. EDSALL 3,157,765

DEAD FRONT FUSE WITH IMPROVED TERMINAL CLAMPING MEANS Filed Dec. 10,1962 2 Sheets-Sheet 1 Nov. 17, 1964 Filed D90. 10, 1962 w. s. EDSALL3,157,766

DEAD FRONT FUSE WITH IMPROVED TERMINAL CLAMPING MEANS 2 Sheets-Sheet 2United States Patent 3,157,766 DEAD FRQNT FUiE W TMPRQVED TERMTNALQLAMPTNG lidEANh William S. Edsali, Boston, Mass, assignor to TheShawrnut Company, New! uryport, Mass.

Filed Bee. it), 1962, No. 24 3,483 2 Claims. (8i. 2tl l132) Thisinvention relates to electric fuses, and more particularly to so-calleddead-front electric fuses.

Conventional electric fuses--be it fuses of the ferrule type, or fusesof the blade type-are normally applied in connection with fuse holdershaving exposed contacts, and such fuses are intended to be applied inconnection with such fuse holders. The provision of exposed confacts isan ever present danger to maintenance personnel, particularly ininstances where such personnel is not highly skilled, in damp locations,and where the circuit voltage is relatively high.

It is, therefore, one object of this invention to provide electric fusesprecluding immediate access to the contact structures thereof and thuseliminating the danger to human life and safety resulting from theprovision of exposed or readily accessible contact structures.

Arrangements of fuses and fuse holders wherein all live parts arearranged on the rear side and are inaccessible from the front side ofthe fuses, are referred to as dead-front arrangements.

It is another object of this invention to provide in proved dead-frontfuse and fuse holder arrangements.

Generally dead-front fuse and fuse holder arrangements involve shroudsupporting the fuse and shielding the contacts thereof. Such arrangementsare, however, relatively bulky and relatively expensive.

It is, therefore, another object of this invention to provideshroudless, compact and relatively inexpensive dead-front fuses.

Prior art dead-front fuses lend themselves to low current ratings aswell as to high current ratings.

Other objects and advantages of the invention will become apparent tothose versed in the art upon making reference to the ensuing descriptionand drawings in which a preferred structural embodiment of the inventionis shown by Way of illustrative example.

In the drawings:

FIG. 1 is mainly a section along lll of FIG. 2 and shows an electricfuse and a cooperating fuse holder forming part of a panelboard, someparts of the structure being shown in elevation rather than in section;

FIG. 2 is mainly a section along of FIG. 1, some parts being showntherein in elevation rather than in section; and

FIG. 3 is a section along 3-3 of FIG. 1, some of the parts of FIG. 3being again shown in elevation rather than in section.

Referring now to the drawings, numerm 1 has been up pllied to indicate acasing of insulating material having a predetermined length L andforming a pair of annular rims 1:: at the axially outer ends thereof.Casing i may be of a melamine-glass-cloth laminate. it houses a pair ofspaced aligned electric terminals in form of plates or blocks 4..Reference letter i has been. applied to indicate the spacing betweenterminals or terminal plates or blocks 4. It is apparent that the latteris less than the length L of easing l, i.e.

L' L Terminals d are arranged in their entirety inside of housing 1, thelatter being closed on both ends thereof by insulating plugs 3,preferably made of a fairly heat resistant synthetic resin. Each ofinsulating plugs 3 supports one of terminals 4 in a fashion set forthbelow more in detail.

3,l57,766 Patented Nov. 17, 1964 Each insulating plug 3 comprises anaxially inner portion 3:: having a relatively small outer diameter andfitted into casing 1 and an axially outer portion 311 having arelatively large outer diameter. The axially outer portion 35b of eachplug 3 abuts against one of the annular rims fa of casing 1 and iscemented to it by a cement having a relatively high tensile strength.Each insulating plug 3 is provided with a recess 30 extending in adirection longitudinally of casing 1 and closed at the axially outer endthereof. Thus recesses 3c form dead-end passageways. Each recess 30accommodates a terminal element or terminal block l, preferably formedby a rectangular stamping of bar copper. Each insulating plug 3 isfurther provided with a bore 3d formin a pasageway extending radiallywith respect to casing 1 and at right angles to the eneral plane definedby terminal plates 4. Terminal plates 4 are conductively interconnectedby a pair of spaced ribbon fuse links 5 of copper or silver, eacharranged at opposite sides of terminal plates 4 and sandwiching theaxially inner ends of terminal plates 4. Fuse links 5 comprise aplurality of transverse lines So of circular perforations and each fuselink 5 supports an overlay 5b of a link-severing low fusing point metal,e.g. tin. Regarding the geometry and arrangement of overlays 5b on fuselinks 5, I prefer to follow the teaching given in U.S. Patent 2,988,620to F. l. Kozacka, Time-Lag Fuses, issued June 13, 1961, and referencemay be had to that patent as to particulars of the geometry andarrangement of overlays 5b. Fuse links 5 are submersed in a pulverulentarc-quenching filler 6 such as, for instance, quartz sand. Each terminalplate 4 is provided with a hole or bore 4a which is internallyscrew-threaded and receives the radially inner end of a screw-threadedbolt or stud 7 forming part of a stab-connector or stab contact. Bolt orstud '7 is arranged inside of bore 3d in each insulating plug 3 and hasa radially outer screw-threaded end supporting a current-carryingcontact 8. The radially inner end of current-carrying contact 8 restsagainst a washer 9 which, in turn, rests against an insulating member 10hugging the outer surface of casing 1. The radially inner end surface ofcontact 8 presses against washer 9 which, in turn, compresses insulatingmember 10. The higher the pressure upon insulating member 10, thetighter the sealing effect thereof limiting venting of products ofarcing from the inside of casing 1 to the outside thereof. As a generalrule, a limited degree of venting of products of arcing from casing Itis believed to be desirable.

Current carrying contacts may be provided with a transverse bore So forreceiving a key or tool for screwing contact 8 against parts 9, 10.

it will be understood that bolts or studs 7 are normally under tensionand insulating plugs 3 are normally under compression.

(Zurrent carrying contacts 8 engage a pair of tulip type contacts ll.Contacts 11 are made up of a plurality of stampings 11a arranged in acircular pattern around contacts 8 and kept in engagement under pressurewith contacts 8 by garter springs 11b. Garter springs 11b cause alsoengagement under pressure of stampings 11a with current carrying studs11c. Tulip type contacts 11 may be accommodated in an insulating housing2 closed by a front panel 12 of insulating material having a pair ofapertures 12a for the passage of stab connectors 7, 8.

When assembling a structure embodying this invention a subassemblycomprising fuse links 5 and terminal plates 4 is inserted into casing 1and then one side of casing 1 is closed by an insulating plug 3 and thatplug is held in position by insertion of a stab connector assembly 7, 8.Thereafter filler 6 is poured into casing 1, the latter is closed bysecond insulating plug 3, and the latter is held in position byinsertion of the second stab connector assembly 7, 3.

It will be understood that I have illustrated and described herein apreferred embodiment of my invention, and that various alterations mayhe made therein without departing from the spirit and scope of theappended claims.

I claim as my invention:

1. An electric dead-front fuse comprising:

(a) .a tubular casing of insulating material having a predeterminedinner diameter and a predetermined length and forming a pair of annularrims at the axially outer ends thereof;

(b) ribbon-shaped fuse link'means having a predetermined thicknessarranged inside of said casing extending in a direction longitudinallythereof;

(c) a pair of insulating plugs having axially inner ends of relativelysmall diameter equal to said predetermined inner diameter of said casingfitted into said casing and having axially outer ends equal in di ameterto the outer diameter of said casing and arranged in abutting relationto said pair of rims, each of said pair of plugsdefining an axiallyextending recess closed at the axially outer end thereof and open at theaxially inner end thereof, and each of said pair of plugs definingaradialpassageway having a radially inner end communicating with saidrecess;

(d) a pair oft'erminal blocks each having a thickness being a multipleof said predetermined thickness of said fuse link means and each beinginserted into said axially extending recess of one of said pair ofinsulating plugs, each of said pair of terminal blocks defining aradially extending internally screwthreaded passageway in registry withsaid radial passageway in one of said pair of insulating plugs;

(e) means conductively connecting each of the axially outer ends of saidfuse link means to one of said pair of terminal blocks;

(f) a pair of studs each projecting transversely through said casing andthrough said radial passageway in one of said pair of insulating plugs,each of said pair of studs having a radially inner screw-threaded endcooperatively engaging said internally screw-thread ed passageway in oneof said pair of insulating plugs, and each of said pair of studs havinga radially outer screw-threaded end; and

(g) a pair of screw nuts each mounted on said radially outerscrew-threaded end of one of said pair of studs and each stressing oneof said pair of studs in a direction longitudinally thereof and therebyclamping one of said pair of terminal blocks in position inside saidrecess of one of said pair of insulating plugs, each of said pair ofscrew nuts having an outer substantially cylindrical contact surface.

2. An electric dead-front fuse comprising:

(a) a tubular casing of insulating material having a predetermined innerdiameter and a predetermined length and forming a pair of annular rimsat the axially outer ends thereof;

(b) ribbon-shaped fuse link means having a predetermined thicknessarranged inside of said casing extending in a direction longitudinallythereof;

(c) a pair of insulating plugs having axially inner ends of relativelysmall diameter equal to said predetermined inner diameter of said casingfitted into said casing and having axially outer ends equal in diameterto the outer diameter of said casingand arranged in abutting relation tosaid pair of rims, each of said pair of plugs defining an axiallyextending recess closed at the axially outer end thereof and open at theaxially inner end thereof, and each of said pair of plugs defining aradial passageway having a radially inner end communicating with saidrecess;

(d) a pair of terminal blocks each having a thickness being a multipleof said predetermined thickness of said fuse link means and each beinginserted into said axially extending recess of one of said pair ofinsulating plugs, each of said pair of terminal blocks defining aradially extending internally screw-threaded passageway in registry withsaid radial passageway in one of said pair of insulating plugs;

(6) means conductively connecting each of the axially outer ends of saidfuse link means to one of said pair of terminal blocks;

(f) a'pair -of studs each projecting transversely through said casingand through said radial passageway in one of said pair of insulatingplugs, each of said pair of studs having a radially'inner screw-threadedend cooperatively engaging said internally screwthreaded passageway inone of said pair of insulating plugs, and each of said pair of studshaving a radially outer screw-threaded end;

(g) a pair of substantially cylindrical contact mem-- bers each havingan axial internally screw-threaded bore, each of said pair of contactmembers being mounted on said radially outer screw-threaded end of oneof said pair of studs stressing one of said pair of studs in a directionlongitudinally thereof and thereby clamping one of said pair of terminalblocks in position inside said recess of one of said pair of insulatingplugs; and

(h) a pair of compressible seal-s each mounted on one of said pair ofstuds and each interposed between the outer surface of said casing andone of said pair of contact members to limit the flow of products ofarcing along said pair of studs out of said casing.

References Cited by the Examiner UNrrED STATES PATENTS BERNARD A.GILHEANY, Primary Examiner.

iiii Julius is is I V I i W flilfii of. ii I I UNITED STATES RATENTOFFICE CERTIFICATE OF CORRECTION Patent No. 3, 157,766 November 17, 1964William 5. Ed sall It is hereby certified that error appears in theabove numbered patent requiring correction and that the said LettersPatent should read as corrected below.

Column 1, lines 38 and 39, strike out "Prior art deadfront fuses lendthemselves to low current ratings as well as to high current ratings.column 2, line 14, for "pasageway" read passageway column 3, line 43,andocolumn 4, lines 31 and 32, for "insulating plugs", each occurrence,read terminal blocks Signed and sealed this 13th day of April 1965,

(SEAL) Attest:

ERNEST W. SWIDER' EDWARD J. BRENNER Attesting Officer Commissioner ofPatents UNITED STATES RATENT OFFICE CERTIFICATE OF CORRECTION William S.Edsall s in the above numbered petthat error appear nt should read as Itis hereby certified ent requiring correction and that the said LettersPate corrected below.

Column 1 lines 38 and 39, strike out "Prior art deadtings as well asfront fuses lend themselves to low current ra for "pasageway" to highcurrent ratingsg"; column 2, line l4 read passageway column 3, line 43,andocolumn 41, lines 31 and 32, for "insulating plugs", each occurrenceread terminal blocks Signed and sealed this 13th day of April 1965.,

(SEAL) Attest:

EDWARD J. BRENNER ERNEST W. SWIDER' I Avttesting Officer Comm ssioner ofPatents

1. AN ELECTRIC DEAD-FRONT FUSE COMPRISING: (A) A TUBULAR CASING OFINSULATING MATERIAL HAVING A PREDETERMINED INNER DIAMETER AND APREDETERMINED LENGTH AND FORMING A PAIR OF ANNULAR RIMS AT THE AXIALLYOUTER ENDS THEREOF; (B) RIBBON-SHAPED FUSE LINK MEANS HAVING APREDETERMINED THICKNESS ARRANGED INSIDE OF SAID CASING EXTENDING IN ADIRECTION LONGITUDINALLY THEREOF; (C) A PAIR OF INSULATING PLUGS HAVINGAXIALLY INNER ENDS OF RELATIVELY SMALL DIAMETER EQUAL TO SAIDPREDETERMINED INNER DIAMETER OF SAID CASING FITTED INTO SAID CASING ANDHAVING AXIALLY OUTER ENDS EQUAL IN DIAMETER TO THE OUTER DIAMETER OFSAID CASING AND ARRANGED IN ABUTTING RELATION TO SAID PAIR OF RIMS, EACHOF SAID PAIR OF PLUGS DEFINING AN AXIALLY EXTENDING RECESS CLOSED AT THEAXIALLY OUTER END THEREOF AND OPEN AT THE AXIALLY INNER END THEREOF, ANDEACH OF SAID PAIR OF PLUGS DEFINING A RADIAL PASSAGEWAY HAVING ARADIALLY INNER END COMMUNICATING WITH SAID RECESS; (D) A PAIR OFTERMINAL BLOCKS EACH HAVING A THICKNESS BEING A MULTIPLE OF SAIDPREDETERMINED THICKNESS OF SAID FUSE LINK MEANS AND EACH BEING INSERTEDINTO SAID AXIALLY EXTENDING RECESS OF ONE OF SAID PAIR OF INSULATINGPLUGS, EACH OF SAID PAIR OF TERMINAL BLOCKS DEFINING A RADIALLYEXTENDING INTERNALLY SCREWTHREADED PASSAGEWAY IN REGISTRY WITH SAIDRADIAL PASSAGEWAY IN ONE OF SAID PAIR OF INSULATING PLUGS; (E) MEANSCONDUCTIVELY CONNECTING EACH OF THE AXIALLY OUTER ENDS OF SAID FUSE LINKMEANS TO ONE OF SAID PAIR OF TERMINAL BLOCKS; (F) A PAIR OF STUDS EACHPROJECTING TRANSVERSELY THROUGH SAID CASING AND THROUGH SAID RADIALPASSAGEWAY IN ONE OF SAID PAIR OF INSULATING PLUGS, EACH OF SAID PAIR OFSTUDS HAVING A RADIALLY INNER SCREW-THREADED END COOPERATIVELY ENGAGINGSAID INTERNALLY SCREW-THREADED PASSAGEWAY IN ONE OF SAID PAIR OFINSULATING PLUGS, AND EACH OF SAID PAIR OF STUDS HAVING A RADIALLY OUTERSCREW-THREADED END; AND (G) A PAIR OF SCREW NUTS EACH MOUNTED ON SAIDRADIALLY OUTER SCREW-THREADED END OF ONE OF SAID PAIR OF STUDS AND EACHSTRESSING ONE OF SAID PAIR OF STUDS IN A DIRECTION LONGITUDINALLYTHEREOF AND THEREBY CLAMPING ONE OF SAID PAIR OF TERMINAL BLOCKS INPOSITION INSIDE SAID RECESS OF ONE OF SAID PAIR OF INSULATING PLUGS,EACH OF SAID PAIR OF SCREW NUTS HAVING AN OUTER SUBSTANTIALLYCYLINDRICAL CONTACT SURFACE.